Single screw compressors used as compressors for refrigeration and air conditioning have been known. For example, the single screw compressor shown in Japanese Patent Publication No. 2004-324601 includes a screw rotor having a plurality of helical grooves on the outer peripheral surface thereof, and two gate rotors each of which is in the shape of a flat plate and having a plurality of teeth. The two gate rotors are arranged such that the axis of each of the gate rotors is orthogonal to the axis of the screw rotor, and are placed symmetrically with respect to the screw rotor. Further, two compression chambers are formed by being surrounded by an inner peripheral surface of a cylindrical wall, a tooth groove of the screw rotor, and the teeth of the gate rotors.
In this single screw compressor, the teeth of the gate rotors move along the tooth groove of the screw rotor as the screw rotor rotates, and the operation in which the capacity of each of the compression chambers is increased and decreased is repeated. During a period when the capacity of the compressor is increased, a refrigerant is sucked in the compression chamber, and when the capacity of the compression chamber starts to decrease, the sucked refrigerant is compressed. When the tooth groove (i.e., the compression chamber) communicates with an outlet, the compressed high-pressure refrigerant is discharged from the compression chamber.